At one time, I suffered lower back pain that was bad enough to land me in physical therapy... not once but twice. I finally got the message and did two things: started swimming laps and in doing so, lost weight.
Losing 30 pounds and continuing my regular lap swimming (2-3x/week) has kept the ache away. I'd recommend swimming to anyone who suffers from lower back pain. It doesn't take much to whack that pain. I swim for just a half an hour and, if I have the time, I sit in the hot tub for a minute or two afterward.
In the new Chicken Soup book, Say Goodbye to Back Pain,
I write about my hassle with back pain and my solution. It's a funny story about how I got to the point of not being able to pick up my child because of the pain, and what I had to do one day when I had to get him, kicking and squalling, to the car when he didn't want to leave the park. There are some great stories, and great solutions, in this book. Maybe one will help you, too.